In the vacuum evaporization of metals such coatings as anticorrosive, wear-resistant, refractory, antifriction, superconductive, optical etc. are produced.
Vacuum application of coatings can be carried out by means of an electron-beam apparatus, wherein metal vapour is formed in evaporization of metals from crucibles by an electron beam. The use of crucibles does not permit producing coatings from refractory metals. Moreover, the coatings thus obtained are contaminated by a crucible material.
The vacuum-arc plasma apparatus makes it possible to produce pure coatings from any metals, refractory ones among them.
In such an apparatus a consumable cathode is evaporized by means of an arc discharge, a plasma flow of the metal vapor is formed, said metal being in a highly ionized state at a high value of energy and concentration of particles, and in the following condensation thereof forming a coating.
Vacuum-arc plasma apparatuses create a diverging plasma flow of a material being evaporized, the coefficient of utilization of the plasma flow in the application of coatings being low. The plasma flow of the material being evaporized is to be focused to produce coatings.
Known in the art is a vacuum-arc apparatus (USSR Author's Certificate No. 416,789 issued 25 Nov. 1974), comprising a consumable cathode, an anode disposed coaxially therewith, and an igniting electrode.
An arc discharge between the consumable cathode and the anode is excited by means of the igniting electrode.
The consumable cathode generates a wide divergent flow of metallic plasma, and thus the efficiency of utilization of the material being evaporized for producing coatings is low. For this reason the utilization of the above apparatus for vacuum metallization is inexpedient.
Also known in the art is an impulse generator of metallic plasma (A. S. Gilmour, D. L. Lochwood. Pulsed metallic-plasma generators, Proc. JEEE, 60 , 8, 977, 1972), comprising a consumable cathode, a solenoid disposed coaxially therewith, and an anode disposed within the solenoid and an igniting electrode. The igniting electrode encircles the consumable cathode and is separated therefrom by an insulator. The ignition of an arc discharge is accomplished by a current pulse causing evaporization of a conductive film from the surface of said insulator. The film is restored during the burning of the arc discharge. The flow of metallic plasma, generated by the consumable cathode, is focused by an axially-symmetrical magnetic field of the solenoid, thereby acquiring a narrower directional diagram.
The above apparatus increases the efficiency of utilization of the evaporized material of a consumable cathode. However, an increase in the flow of the evaporized material of a consumable cathode at the outlet of the apparatus is limited by a partial reflection of ions from a magnetic barrier created at the ends of the solenoid. Moreover, the above generator is not suitable for operation in a stationary operation mode because of design features of igniting electrode.
Known in the art is a vacuum-arc plasma apparatus allowing the efficiency of utilization of the evaporized material of a consumable cathode to be increased in a stationary operation mode (I. I. Aksenov, V. G. Padalka, V. T. Toloka, V. M. Khoroshikh. Fokusirovka potoka metallicheskoi plazmy, generiruyemogo statsionarnym erozionnym elektrodugovym uskoritelem, sb. "Istochniki i uskoriteli plasmy, Vyp. 3, Kharkov, 1978, s. 45-50).
The apparatus comprises a consumable cathode having a working end face, a solenoid being coaxial therewith, a tubular anode disposed within the solenoid, and an igniting electrode.
In this apparatus, the igniting electrode excites an arc discharge. The flow of metallic plasma, generated by the consumable cathode, is focused by an axially-symmetric magnetic field of the solenoid. Such an arrangement permits obtaining a narrower directional diagram of the metal being evaporized and increasing the efficiency of utilization thereof.
However, in the above device a portion of the ion component of the plasma flow is reflected from an electromagnetic barrier occuring in the operation of the device due to the deviation of magnetic lines of force at the end face of the solenoid, said portion missing the substrate. Another disadvantage of the above device is an unstable ignition and burning of the arc discharge, which can be explained by the following reasons. In the case of location of the igniting electrode at the working end of the consumable cathode there occur failures in the operation because of the damage of the igniting electrode caused by a stationary arc discharge. The igniting electrode being disposed at a side surface of the consumable cathode, the stability of the ignition process is disturbed since a cathode spot being excited on the side surface is thrown by the magnetic field of the solenoid to the side opposite to the working end of the consumable cathode. Such "throwing aside" terminates with extinction of the arc discharge. Spontaneous "runnings-out" of the cathode spot from the working end of the consumable cathode to the side surface thereof terminate in a similar way.